Method of monitoring membrane separation processes

ABSTRACT

Methods and systems for monitoring and/or controlling membrane separation systems or processes are provided. The present invention utilizes measurable amounts of inert fluorescent tracer(s) added to a feed stream to evaluate and/or control the purification of such feed stream during membrane separation. The methods and systems of the present invention can be utilized in a variety of different industrial applications including raw water processing and waste water processing.

FIELD OF THE INVENTION

This invention relates generally to membrane separation and, moreparticularly, to methods for monitoring and/or controlling membraneseparation processes.

BACKGROUND OF THE INVENTION

Membrane separation, which uses a selective membrane, is a fairly recentaddition to the industrial separation technology for processing ofliquid streams, such as water purification. In membrane separation,constituents of the influent typically pass through the membrane as aresult of a driving force(s) in one effluent stream, thus leaving behindsome portion of the original constituents in a second stun. Membraneseparations commonly used for water purification or other liquidprocessing include microfiltration (MF), ultrafiltration (UF),nanofiltration (NF), reverse osmosis (RO), electrodialysis,electrodeionization, pervaporation, membrane extraction, membranedistillation, membrane stripping, membrane aeration, and otherprocesses. The driving force of the separation depends on the type ofthe membrane separation. Pressure-driven membrane filtration, also knownas membrane filtration, includes microfiltration, ultrafiltration,nanofiltration and reverse osmosis, and uses pressure as a drivingforce, whereas the electrical driving force is used in electrodialysisand electrodeionization. Historically, membrane separation processes orsystems were not considered cost effective for water treatment due tothe adverse impacts that membrane scaling, membrane fouling, membranedegradation and the like had on the efficiency of removing solutes fromaqueous water streams. However, advancements in technology have now mademembrane separation a more commercially viable technology for treatingaqueous feed streams suitable for use in industrial processes.

Furthermore, membrane separation processes have also been made morepractical for industrial use, particularly for raw and wastewaterpurification. This has been achieved through the use of improveddiagnostic tools or techniques for evaluating membrane separationperformance. The performance of membrane separation, such as efficiency(e.g. flux or membrane permeability) and effectiveness (e.g. rejectionor selectivity), are typically affected by various parameters concerningthe operating conditions of the process. Therefore, it is desirable tomonitor these and other types of process parameters specific to membraneseparation to assess the performance of the process and/or the operatingconditions. In this regard, a variety of different diagnostic techniquesfor monitoring membrane separation processes have been routinely usedand are now understood and accepted as essential to its practicality andviability for industrial use.

However, monitoring is typically conducted on an intermittent basis, forexample, once a work shift or at times less frequently. Known employedmonitoring techniques can also be labor and time intensive. Thus,adjustments made to membrane separation processes in order to enhanceperformance based on typical monitoring may not be made in anexpeditious manner. In addition, the presently available monitoringtechniques often do not provide optimal sensitivity and selectivity withrespect to monitoring a variety of process parameters that are generallyrelied on as indicators to evaluate and/or control membrane separationprocesses.

For example, monitoring techniques typically applied to reverse osmosisand nanofiltration include conductivity measurements and flowmeasurements. Conductivity measurements are inherently less accurate inorder to determine the recovery of solutes which are substantiallyretained by the membrane. In this regard, conductive salts, typicallyused as indicators during conductive measurements, can pass through themembrane. Since salts generally pass through the membrane as apercentage of the total salt concentration, changes in localconcentration due to concentration gradients or the like can change theconductivity of the product water without necessarily indicatingmembrane damage. This is especially true in the last stage of amulti-stage cross flow membrane system where salt concentrations (and,therefore, passage of salts as a percentage of that concentration) reachtheir highest levels. In this regard, the salt passage/percent rejectionparameter is generally determined as an average value based on valuesmeasured during all stages of the membrane system.

Further, flow meters generally employed in such systems are subject tocalibration inaccuracies, thus requiring frequent calibration. Moreover,typical monitoring of reverse osmosis and other membrane separations canroutinely require the additional and/or combined use of a number ofdifferent techniques, thus increasing the complexity and expense ofmonitoring.

Accordingly, a need exists to monitor and/or control membrane separationprocesses which can treat feed streams, such as aqueous feed streams,suitable for use in industrial processes where conventional monitoringtechniques are generally complex and/or may lack the sensitivity andselectivity necessary to adequately monitor one or more processparameters specific to membrane separation processes which are importantto the evaluation of the performance of membrane separation.

SUMMARY OF THE INVENTION

The present invention provides methods and systems for monitoring and/orcontrolling membrane separation processes capable of treating feedstreams suitable for use in industrial processes. In this regard, thedetection of inert fluorescent tracers is utilized to evaluate and/orcontrol a number of different process parameters unique to membraneseparation, such as operational parameters, chemical parameters,mechanical parameters, and combinations thereof. The inert fluorescenttracer monitoring technique of the present invention can be performedwith a high degree of sensitivity and selectivity with respect to themonitoring of process parameters specific to a membrane separation. Inthis regard, the methods and systems of the present invention can beeffectively utilized to optimize the performance of membrane separationprocesses. Examples of such optimized performance include longer timesbetween membrane cleanings, longer membrane life, verification oftreatment chemical in the system, ability to operate at optimalrecovery, and decreased energy costs due to better control of scaling,fouling and other system parameters.

To this end, in an embodiment of the present invention, a method ofmonitoring a membrane separation process including a membrane capable ofseparating a feed stream into at least a first stream and a secondstream is provided. The method includes the steps of providing an inertfluorescent tracer; introducing the inert fluorescent tracer into thefeed stream; providing a fluorometer to detect the fluorescent signal ofthe inert fluorescent tracer in at least one of the feed stream, thefirst stream and the second stream; and using the fluorometer todetermine an amount of the inert fluorescent tracer in at least one ofthe feed stream, the first stream and the second stream.

In another embodiment, a method of monitoring a membrane separationsystem including a membrane capable of removing solutes from a feedstream suitable for use in an industrial process is provided. The methodincludes the steps of adding an inert tracer to the feed stream;contacting the membrane with the feed stream; separating the feed streaminto a permeate stream and a concentrate stream to remove solutes fromthe feed stream; providing a fluorometer to detect the fluorescentsignal of the inert tracer in at least one of the feed stream, thepermeate stream and the concentrate stream; and using the fluorometer tomeasure an amount of the inert tracer in at least one of the feedstream, the permeate stream and the concentrate stream.

In yet another embodiment, a membrane separation system capable ofpurifying an aqueous feed stream suitable for use in an industrialprocess is provided. The membrane separation system includes asemi-permeable membrane capable of separating the aqueous feed streamcontaining an inert tracer into a permeate stream and a concentratestream to remove one or more solutes from the aqueous feed stream; adetection device capable of fluorometrically measuring an amount of theinert tracer ranging from about 5 parts per trillion (“ppt”) to about1000 parts per million (“ppm”) in at least one of the aqueous feedstream, the permeate stream and the concentrate stream wherein thedetection device is capable of producing a signal indicative of theamount of inert tracer that is measured, and a controller capable ofprocessing the signal to monitor and/or control the purification of theaqueous feed stream. Such monitoring or control may include control ofchemical dosing and checking the accuracy/calibration of standardinstruments (e.g. flow sensors).

In still another embodiment, a method of monitoring and controlling amembrane separation process including a membrane capable of removingsolutes from a feed stream for use in an industrial process is provided.The method includes the steps of adding an inert tracer to the feedstream; contacting the membrane with the feed stream; separating thefeed stream into a first effluent stream and a second effluent stream toremove solutes from the feed stream; providing a fluorometer to detectthe fluorescent signal of the inert tracer in at least one of the feedstream, the first effluent stream and the second effluent stream; usingthe fluorometer to measure an amount of the inert tracer ranging fromabout 5 ppt to about 1000 ppm in at least one of the feed stream, thefirst effluent stream and the second effluent stream; and evaluating oneor more process parameters specific to membrane separation based on themeasurable amount of the inert tracer.

It is, therefore, an advantage of the present invention to providemethods and systems that utilize inert fluorescent tracers to monitorand/or control membrane separation processes or systems.

Another advantage of the present invention is to provide methods andsystems that utilize measurable amounts of inert tracers to improve theoperational efficiency of membrane separation processes or systems.

A further advantage of the present invention is to provide methods andsystems for monitoring parameters specific to membrane separationprocesses with selectivity and specificity based on measurable amountsof inert tracers added to the membrane separation system.

Yet another advantage of the present invention is to provide methods andsystems for monitoring and/or controlling membrane separation processesfor purifying aqueous feed streams suitable for use in industrial watersystems.

Still further an advantage of the present invention is to provide animproved performance specific to membrane separation processes orsystems that utilize cross-flow and/or dead-end flow separation toremove solutes from feed streams.

Additional features and advantages of the present invention aredescribed in, and will be apparent in, the detailed description of thepresently preferred embodiments.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention provides methods and systems for monitoring and/orcontrolling membrane separation processes that are capable of removingsolutes from feed streams, such as aqueous feed streams, which aresuitable for use in a number of different industrial applications. Morespecifically, the methods and systems of the present invention canmonitor and/or control membrane separation processes based on measurableamounts of inert fluorescent tracers which have been added to themembrane separation process. In this regard, a number of differentprocess parameters specific to membrane separation; including, forexample, operational parameters, chemical parameters, mechanicalparameters, like parameters and combinations thereof, can be evaluatedwith a high degree of selectivity, specificity and accuracy such thatthe performance of the membrane separation process can be effectivelyoptimized.

The methods and systems of the present invention can include a varietyof different and suitable components, process steps, operatingconditions and the like, for monitoring and/or controlling membraneseparation processes or systems. In an embodiment, the membraneseparation process of the present invention includes cross flow anddead-end flow processes. During cross flow processes, the feed streamcan be treated in a flow direction that is substantially parallel to themembrane of the separation system. With respect to dead-end flowseparation processes, the feed stream can be treated in a flow directionthat is substantially perpendicular to the membrane of the separationsystem.

In general, the membrane separation processes of the present inventionare capable of treating or purifying feed streams by dividing the feedstream into separate streams. In an embodiment, the feed stream isseparated into at least a first and second stream, such as a permeatestream and a concentrate stream. The feed stream can contain varioussolutes, such as dissolved organics, dissolved inorganics, dissolvedsolids, suspended solids, the like or combinations thereof Uponseparation of the feed stream into the permeate and the concentrate, inmembrane filters for example, the permeate stream essentially contains asubstantially lower concentration of dissolved and/or suspended solutesas compared to the aqueous feed stream. On the other hand, theconcentrate stream has a higher concentration of dissolved and/orsuspended solutes as compared to the aqueous stream. In this regard, thepermeate represents a purified feed stream, such as a purified aqueousfeed stream.

It should be appreciated that the present invention can be utilized withrespect to a number of different types of membrane separation processesincluding, for example, cross flow processes, dead-end flow processes,reverse osmosis, ultrafiltration, microfiltration, nanofiltration,electrodialysis, electrodeionization, pervaporation, membraneextraction, membrane distillation, membrane stripping, membrane aerationand the like or combinations thereof. Reverse osmosis, ultrafiltration,microfiltration and nanofiltration are the preferred membrane separationprocesses.

In reverse osmosis, the feed stream is typically processed under crossflow conditions. In this regard, the feed stream flows substantiallyparallel to the membrane surface such that only a portion of the feedstream diffuses through the membrane as permeate. The cross flow rate isroutinely high in order to provide a scouring action that lessensmembrane surface fouling. This can also decrease concentrationpolarization effects (e.g., concentration of solutes in thereduced-turbulence boundary layer at the membrane surface, which canincrease the osmotic pressure at the membrane and thus can reducepermeate flow). The concentration polarization effects can inhibit thefeed stream water from passing through the membrane as permeate, thusdecreasing the recovery ratio, e.g., the ratio of permeate to appliedfeed stream. A recycle loop(s) may be employed to maintain a high flowrate across the membrane surface.

Reverse osmosis processes can employ a variety of different types ofmembranes. Such commercial membrane element types include, withoutlimitation, hollow fiber membrane elements, tubular membrane elements,spiral-wound membrane elements, plate and frame membrane elements, andthe like, some of which are described in more detail in “The Nalco WaterHandbook;” Second Edition, Frank N. Kemmer ed., McGraw-Hill BookCompany, New York, N.Y., 1988, incorporated hereinto, particularlyChapter 15 entitled “Membrane Separation”. It should be appreciated thata single membrane element may be used in a given membrane filtrationsystem, but a number of membrane elements can also be used depending onthe industrial application.

A typical reverse osmosis system is described as an example of membranefiltration and more generally membrane separation. Reverse osmosis usesmainly spiral wound elements or modules, which are constructed bywinding layers of semi-porous membranes with feed spacers and permeatewater carriers around a central perforated permeate collection tube.Typically, the modules are sealed with tape and/or fiberglass over-wrap.The resulting construction has one channel which can receive an inletflow. The inlet stream flows longitudinally along the membrane moduleand exits the other end as a concentrate stream. Within the module,water passes through the semi-porous membrane and is trapped in apermeate channel which flows to a central collection tube. From thistube it flows out of a designated channel and is collected.

In practice, membrane modules are stacked together, end to end, withinter-connectors joining the permeate tubes of the first module to thepermeate tube of the second module, and so on. These membrane modulestacks are housed in pressure vessels. Within the pressure vessel feedwater passes into the first module in the stack, which removes a portionof the water as permeate water. The concentrate stream from the firstmembrane becomes the feed stream of the second membrane and so on downthe stack. The permeate streams from all of the membranes in the stackare collected in the joined permeate tubes. Only the feed streamentering the first module, the combined permeate stream and the finalconcentrate stream from the last module in the stack are commonlymonitored.

Within most reverse osmosis systems, pressure vessels are arranged ineither “stages” or “passes.” In a staged membrane system, the combinedconcentrate streams from a bank of pressure vessels are directed to asecond bank of pressure vessels where they become the feed stream forthe second stage. Commonly systems have 2 to 3 stages with successivelyfewer pressure vessels in each stage. For example, a system may contain4 pressure vessels in a first stage, the concentrate streams of whichfeed 2 pressure vessels in a second stage, the concentrate streams ofwhich in turn feed 1 pressure vessel in the third stage. This isdesignated as a “4:2:1” array. In a staged membrane configuration, thecombined permeate streams from all pressure vessels in all stages arecollected and used without further membrane treatment. Multi-stagesystems are used when large volumes of purified water are required, forexample for boiler feed water. The permeate streams from the membranesystem may be further purified by ion exchange or other means.

In a multi-pass system, the permeate streams from each bank of pressurevessels are collected and used as the feed to the subsequent banks ofpressure vessels. The concentrate streams from all pressure vessels arecombined without further membrane treatment of each individual stream.Multi-pass systems are used when very high purity water is required, forexample in the microelectronics or pharmaceutical industries.

It should be clear from the above examples that the concentrate streamof one stage of an RO system can be the feed stream of another stage.Likewise the permeate stream of a single pass of a multi-pass system maybe the feed stream of a subsequent pass. A challenge in monitoringsystems such as the reverse osmosis examples cited above is that thereare a limited number of places where sampling and monitoring can occur,namely the feed, permeate and concentrate streams. In some, but not all,systems “inter-stage” sampling points allow sampling/monitoring of thefirst stage concentrate/second stage feed stream. Similar inter-passsample points may be available on multi-pass systems as well.

In practice it is possible to “probe” the permeate collection tubewithin a single pressure vessel to sample the quality of the permeatefrom each of the membrane elements in the stack It is a time consuming,messy and inexact method and is not routinely applied except introubleshooting situations. There is no currently accepted method ofexamining the feed/concentrate stream quality of individual membraneelements within a single pressure vessel.

In contrast to cross-flow filtration membrane separation processes,conventional filtration of suspended solids can be conducted by passinga feed fluid through a filter media or membrane in a substantiallyperpendicular direction. This effectively creates one exit stream duringthe service cycle. Periodically, the filter is backwashed by passing aclean fluid in a direction opposite to the feed, generating a backwasheffluent containing species that have been retained by the filter. Thusconventional filtration produces a feed stream, a purified stream and abackwash stream. This type of membrane separation is typically referredto as dead-end flow separation and is typically limited to theseparation of suspended particles greater than about one micron in size.

Cross-flow filtration techniques, on the other hand, can be used forremoving smaller particles (generally about one micron in size or less),colloids and dissolved solutes. Such types of cross-flow membraneseparation systems can include, for example, reverse osmosis,microfiltration, ultrafiltration, nanofiltration, electrodialysis or thelike. Reverse osmosis can remove even low molecular weight dissolvedspecies that are at least about 0.0001 to about 0.001 microns in minimumdiameter, including, for example, ionic and nonionic species, lowmolecular weight molecules, water-soluble macromolecules or polymers,suspended solids, colloids, and such substances as bacteria and viruses.

In this regard, reverse osmosis is often used commercially to treatwater that has a moderate to high (e.g., 500 ppm or greater) totaldissolved solids (“TDS”) content. Typically on order of from about 2percent to about 5 percent of the TDS of a feed stream will pass throughthe membrane. Thus, in general the permeate may not be entirely free ofsolutes. In this regard, the TDS of reverse osmosis permeates may be toohigh for some industrial applications, such as use as makeup water forhigh pressure boilers. Therefore, reverse osmosis systems and other likemembrane separation systems are frequently used prior to and incombination with an ion exchange process or other suitable process toreduce the TDS loading on the resin and to decrease the amount ofhazardous material used and stored for resin regeneration, such as acidsand sodium hydroxide.

As discussed above, the performance of membrane separation systems canvary with respect to a number of different operational conditionsspecific to membrane separation, such as temperature, pH, pressure,permeate flow, activity of treatment and/or cleaning agents, foulingactivity and the like. When developing and/or implementing a monitoringand/or control program based on the detection of inert fluorescenttracers, the effects of the operational conditions specific to membraneseparation must necessarily be taken into consideration. As previouslydiscussed, the operational conditions of water treatment processes canvary greatly from process to process. In this regard, the monitoringtechniques as applied to each process can vary greatly.

Membrane separation processes and the monitoring thereof are uniquebecause of the following considerations.

1. Systems are constructed with limited flexibility in terms of wheremonitoring may be done and/or where samples may be collected.

2. Membrane separation systems include a concentration polarizationlayer that forms as water is permeated through the barrier. This is notpresent in other water treatment systems, such as cooling water systems.

3. Membrane separation systems operate at significantly lowertemperatures than industrial processes where inverse solubility ofsolutes is a problem. However, in the case of membrane separationsystems such as reverse osmosis and nanofiltration, this low temperatureleads to scaling from salts that are less likely to be problematic inhigher temperature processes (such as silica and silicate salts). Inthis regard, typical day-to-day membrane separation operations (forexample RO and NF) occur at about 75° F.

4. Because it is essential that the surface of the membrane remainclean, a relatively small amount of fine precipitate can cause asignificant performance loss. The performance loss in a membrane is,thus, more sensitive to precipitate deposition as compared to coolingwater treatment. In this regard, performance loss in a membrane canoccur at a film thickness appreciably lower than that required for heattransfer loss to occur in a cooling water system.

5. Water loss in membrane filtration is due to “permeation” or passagethrough the membrane barrier. Damaged or otherwise imperfect membranesare susceptible to undesirable leakage of solutes through the membrane.Thus it is critical to monitor leakage through the membrane to keep itoperating at maximum efficiency.

6. The thin, semi-permeable films (polymeric, organic or inorganic) aresensitive to degradation by chemical species. Products which contact themembranes surface must be compatible with the membrane chemistry toavoid damaging the surface and thereby degrading performance.

7. Chemical treatments used in membrane systems must be demonstrated tobe compatible with the membrane material prior to use. Damage fromincompatible chemicals can result in immediate loss of performance andperhaps degradation of the membrane surface. Such immediate,irreversible damages from a chemical treatment is highly uncommon incooling water systems.

Based on these differences, a number of different factors andconsiderations must necessarily be taken into account when developingand/or implementing monitoring and/or controlling programs with respectto membrane separation systems as compared to other water treatmentprocesses, such as cooling water treatment processes.

For example, both the cost of the membrane and the energy consumed canbe significant operating cost factors specific to a membrane separationprocess. In this regard, deposits of scale and foulants on the membrane,on a small scale, can adversely impact the performance of membraneseparation systems by, in membrane filtration for example, decreasingthe permeate flow for a given driving force, lowering the permeatequality (purity), increasing energy consumed to maintain a givenpermeate flow, causing membrane replacement and/or unscheduled downtimefor membrane replacement or cleaning/renovation, other like conditionsand combinations thereof. In this regard, the continuous monitoring ofprocess parameters specific to membrane filtration such as normalizedpermeate flow, driving force, differential pressure and percentrejection are generally believed to be critical to the detection offouling and/or scaling and, thus, the implementation of remedialmeasures when such problems are observed. In reverse osmosis, about aten to fifteen percent change in any of these parameters routinelysignals a scaling/fouling problem requiring a responsive action, such asthe adjustment of the dosage of treatment agent. Thus, detection ofthese problems at the earliest possible time can prevent, for example,undue energy consumption, loss of product, premature membranereplacement and the like. Ideally, when an unfavorable or questionablecondition or change is detected in a system, some means, such as analarm, will be used to notify an operator of the condition or change.Corrective action may then be taken as necessary or appropriate.

Applicants have uniquely discovered that the monitoring and/orcontrolling of process parameters specific to membrane separation basedon measuring an amount of inert fluorescent tracer is faster, moresensitive, more comprehensive, more selective and/or more reliable thanconventional techniques presently available, particularly when themonitoring methods of the present invention are employed on asubstantially continuous basis. The present invention has enhanceddiagnostic capabilities such that, for example, lack of chemicaltreatment, unplanned increases in percent recovery, increased passage ofsolutes, flow irregularities and scaling and/or fouling problems uniqueto membrane separation and/or membrane filtration can be detected withreasonable certainty, with far greater sensitivity, and under a far lesselapsed time than the presently available methods. In this regard,temporary system upsets or other short-lived variations can be detectedduring continuous monitoring as the transient conditions that they are,rather than as incorrect warning signs as detected by sporadicmonitorings.

As previously discussed, the methods and systems of the presentinvention employ inert fluorescent tracers to monitor and/or control themembrane separation processes. By utilizing inert tracers, the presentinvention can evaluate a number of different membrane separation processparameters with a greater selectivity and sensitivity as compared toconventional monitoring techniques. In this regard, the measurableamount of inert tracers can be effectively utilized to optimallymaximize the performance of such systems.

The term “inert,” as used herein refers to an inert fluorescent tracerthat is not appreciably or significantly affected by any other chemistryin the system, or by the other system parameters such as pH,temperature, ionic strength, redox potential, microbiological activityor biocide concentration. To quantify what is meant by “not appreciablyor significantly affected”, this statement means that an inertfluorescent compound has no more than a 10% change in its fluorescentsignal, under severe conditions encountered in industrial water systems.Severe conditions normally encountered in industrial water systems areknown to people of ordinary skill in the art of industrial watersystems.

It should be appreciated that a variety of different and suitable inerttracers can be utilized in any suitable amount, number and application.For example, a single tracer can be used to evaluate a number ofdifferent membrane separation process parameters. However, the presentinvention can include the use of a number of different tracers eachfunctioning as tracers for separate monitoring applications. In anembodiment, inert fluorescent tracer monitoring of the present inventioncan be conducted on a singular, intermittent or semi-continuous basis,and preferably the concentration determination of the tracer in thestream is conducted on-site to provide a rapid real-time determination.

An inert tracer must be transportable with the water of the membraneseparation system and thus substantially, if not wholly, water-solubletherein at the concentration it is used, under the temperature andpressure conditions specific and unique to the membrane separationsystem. In other words, an inert tracer displays properties similar to asolute of the membrane separation process in which it is used. In anembodiment, it is preferred that the inert tracer of the presentinvention meet the following criteria:

1. Not be adsorbed by the membrane in any appreciable amount;

2. Not degrade the, membrane or otherwise hinder its performance oralter its composition;

3. Be detectable on a continuous or semi-continuous basis andsusceptible to concentration measurements that are accurate, repeatableand capable of being performed on feedwater, concentrate water, permeatewater or other suitable media or combinations thereof;

4. Be substantially foreign to the chemical species that are normallypresent in the water of the membrane separation systems in which theinert tracer(s) may be used;

3 5. Be substantially impervious to interference from, or biasing by,the chemical species that are normally present in the water of membraneseparation systems in which the inert tracer(s) may be used;

6. Be substantially impervious to any of its own potential specific orselective losses from the water of membrane separation systems,including selective permeation of the membrane;

7. Be compatible with all treatment agents employed in the water of themembrane separation systems in which the inert tracer(s) may be used,and thus in no way reduce the efficacy thereof;

8. Be compatible with all components of its formulation; and

9. Be relatively nontoxic and environmentally safe, not only within theenvirons of the water or the membrane separation process in which it maybe used, but also upon discharge therefrom.

It should be appreciated that the amount of inert tracer to be added tothe membrane separation process that is effective without being grosslyexcessive can vary with respect to a variety of factors including,without limitation, the monitoring method selected, the extent ofbackground interference associated with the selected monitoring method,the magnitude of the expected inert tracer(s) concentration in thefeedwater and/or concentrate, the monitoring mode (such as, an on-linecontinuous monitoring mode), and other similar factors. In anembodiment, the dosage of an inert tracer added to the membraneseparation system includes an amount that is at least sufficient toprovide a measurable concentration in, for example, the concentratestream, at steady state of at least about 5 ppt, and preferably at leastabout 1 ppb or about 5 ppb or higher, such as, up to about 100 ppm orabout 200 ppm, or even as high as about 1000 ppm in the concentrate orother effluent stream. In an embodiment, the amount of tracer rangesfrom about 5 ppt to about 1000 ppm, preferably from about 1 ppb to about50 ppm, more preferably from about 5 ppb to about 50 ppb.

In an embodiment, the inert tracer can be added to a membrane separationsystem as a component of a formulation, rather than as a separatecomponent, such as a dry solid or neat far liquid. The inert tracerformulation or product may include an aqueous solution or othersubstantially homogeneous mixture that disperses with reasonablerapidity in the membrane separation system to which it is added. In thisregard, the inert tracer's concentration may be correlated to theconcentration of a product. In an embodiment, the product or formulationcan include a treatment agent which is added to treat scaling and/orfouling.

A variety of different and suitable types of compounds can be utilizedas inert fluorescent tracers. In an embodiment, the inert fluorescentcompounds can include, for example, the following compounds:

3,6-acridinediamine, N,N,N′,N′-tetramethyl-, monohydrochloride, alsoknown as Acridine Orange (CAS Registry No. 65-61-2),

2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4),

1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and saltsthereof,

2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and saltsthereof,

1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) and saltsthereof,

anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol, 16,17-dimethoxy-,bis(hydrogen sulfate), disodium salt, also known as Anthrasol Green IBA(CAS Registry No. 2538-84-3, aka Solubilized Vat Dye),

bathophenanthrolinedisulfonic acid disodium salt (CAS Registry No.52746-49-3),

amino 2,5-benzene disulfonic acid (CAS Registry No. 41184-20-20-7),

2-(4-aminophenyl)-6-methylbenzothiazole (CAS Registry No. 92-36-4),

1H-benz[de]isoquinoline-5-sulfonic acid,6-amino-2,3dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt, alsoknown as Brilliant Acid Yellow 8G (CAS Registry No. 2391-30-2, akaLissamine Yellow FF, Acid Yellow 7),

phenoxazin-5-ium, 1-(aminocarbonyl)-7diethylamino)-3,4-dihydroxy-,chloride, also known as Celestine Blue (CAS Registry No. 1562-90-9),

benzo[a]phenoxazin-7-ium, 5,9-diamino-, acetate, also known as cresylviolet acetate (CAS Registry No. 10510-54-0),

4-dibenzofuransulfonic acid (CAS Registry No. 42137-76-8),

3-dibenzofuransulfonic acid (CAS Registry No. 215189-98-3),

1-ethylquinaldinium iodide (CAS Registry No. 606-53-3),

fluorescein (CAS Registry No. 2321-07-5),

fluorescein, sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73,Uranine),

Keyfluor White ST (CAS Registry No. 144470-48-4, aka Flu. Bright 28),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Keyfluor White CN (CAS Registry No.16470-24-9),

C.L Fluorescent Brightener 230, also known as Leucophor BSB (CASRegistry No. 68444-86-0),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Leucophor BMB (CAS Registry No.16470-249, aka Leucophor U, Flu. Bright. 290),

9,9′-biacridinium, 10,10′-dimethyl-, dinitrate, also known as Lucigenin(CAS Registy No. 2315-97-1, aka bis-N-methylacridinium nitrate),

1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol,also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5),

mono-, di-, or tri-sulfonated napthalenes, including but not limited to

1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CAS RegistryNo. 1655-29-4, aka 1,5-NDSA hydrate),

2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),

5-amino-2-naphthalenesulfonic acid (CAS Registry No. 119-79-9),

4amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No. 90-51-7),

6amino-4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No. 116-63-2),

7-amino-1,3-naphthalenesulfonic acid, potassium salt (CAS Registry No.79873-35-1),

4amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS Registry No.90-20-0),

5-dimethylamino-1-naphthalenesulfonic acid (CAS Registry No. 4272-77-9),

1-amino-4-naphthalene sulfonic acid (CAS Registry No.84-86-6),

1-amino-7-naphthalene sulfonic acid (CAS Registry No. 119-28-8), and

2,6naphthalenedicarboxylic acid, dipotassium salt (CAS Registry No.2666-06-0),

3,4,9,10perylenetetracarboxylic acid (CAS Registry No. 81-32-3),

C.I. Fluorescent Brightener 191, also known as Phorwite CL (CAS RegistryNo. 12270-53-0),

C.I. Fluorescent Brightener 200, also known as Phorwite BKL (CASRegistry No. 61968-72-7),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No.52237-03-3),

benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Pylaklor White S-15A (CAS Registry No. 6416-68-8),

1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt (CAS Registry No.59572-10-0),

pyranine, (CAS Registry No. 6358-69-6, aka8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt),

quinoline (CAS Registry No. 91-22-5),

3H-phenoxazin-3-one, 7-hydroxy-, 10oxide, also known as Rhodalux (CASRegistry No. 550-82-3),

xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride,disodium salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8),

phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride, also known asSafranine O (CAS Registry No. 477-73-6),

C.I. Fluorescent Brightener 235, also known as Sandoz CW (CAS RegistryNo. 56509-06-9),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Sandoz CD (CAS Registry No. 16470-24-9,aka Flu. Bright. 220),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Sandoz TH40 (CAS Registry No. 32694-95-4),

xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt,sodium salt, also known as Sulforhodamine B (CAS Registry No. 3520-42-1,aka Acid Red 52),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Tinopal 5BM-GX (CAS Registry No.169762-28-1),

Tinopol DCS (CAS Registry No. 205265-33-4),

benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-, disodium saltalso known as Tinopal CBS-X (CAS Registry No. 27344-41-8),

benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),

7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt,also known as Titan Yellow (CAS Registry No. 1829-00-1, aka ThiazoleYellow G), and all ammonium, potassiun and sodium salts thereof, andsuitable mixtures thereof.

Preferred tracers include:

1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol,also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5),

fluorescein (CAS Registry No. 2321-07-5),

fluorescein, sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73,Uranine),

2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4),

1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and saltsthereof,

2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and saltsthereof,

1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) and saltsthereof,

mono-, di-, or tri-sulfonated napthalenes, including but not limited to

1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CAS RegistryNo. 1655-29-4, aka 1,5-NDSA hydrate),

2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),

5-amino-2-naphthalenesulfonic acid (CAS Registry No. 119-79-9),

4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No. 90-51-7),

6-amino4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No. 116-63-2),

7-amino-1,3-naphthalenesulfonic acid, potassiumn salt (CAS Registry No.79873-35-1),

4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS Registry No.90-20-0),

5-dimethylamino-1-naphthalenesulfonic acid (CAS Registry No. 4272-77-9),

1-amino-4-naphthalene sulfonic acid (CAS Registry No. 84-86-6),

1-amino-7-naphthalene sulfonic acid (CAS Registry No. 119-28-8), and

2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS Registry No.2666-06-0),

3,4,9,10-perylenetetracarboxylic acid (CAS Registry No. 81-32-3),

C.I. Fluorescent Brightener 191, also known as, Phorwite CL (CASRegistry No. 12270-53-0),

C.I. Fluorescent Brightener 200, also known as Phorwite BKL (CASRegistry No. 61968-72-7),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4phenyl-2H-1,2,3-triazol-2-yl)-, dipotassiumsalt, also known as Phorwite BHC 766 (CAS Registry No. 52237-03-3),

benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Pylaklor White S-15A (CAS Registry No. 6416-68-8),

1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt (CAS Registry No.59572-10-0),

pyranine, (CAS Registry No. 6358696, aka8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt),

quinoline (CAS Registry No. 91-22-5),

3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as Rhodalux (CASRegistry No. 550-82-3),

xanthylium, 9-(2,4dicarboxyphenyl)-3,6bis(diethylamino)-, chloride,disodium salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8),

phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride, also known asSafranine O (CAS Registry No. 477-73-6),

C.I. Fluorescent Brightener 235, also known as Sandoz CW (CAS RegistryNo. 56509-06-9),

benzenesulfonic acid,2,2′-(1,2ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodiun salt, also known as Sandoz CD (CAS Registry No. 16470-24-9,aka Flu. Bright. 220),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Sandoz TH40 (CAS Registry No. 32694-95-4),

xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt,sodium salt, also known as Sulforhodamine B (CAS Registry No. 3520-42-1,aka Acid Red 52),

benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Tinopal 5BM-GX (CAS Registry No.169762-28-1),

Tinopol DCS (CAS Registry No. 205265-33-4),

benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-, disodium salt,also known as Tinopal CBS-X (CAS Registry No. 27344-41-8),

benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),

7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt,also known as Titan Yellow (CAS Registry No. 1829-00-1, aka ThiazoleYellow G), and

all ammonium, potassium and sodium salts thereof, and all like agentsand suitable mixtures thereof.

The most preferred fluorescent inert tracers of the present inventioninclude 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (CAS RegistryNo. 59572-10-0); 1,5-naphthalenedisulfonic acid disodium salt (hydrate)(CAS Registry No. 1655-29-4, aka 1,5-NDSA hydrate); xanthylium,9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt,also known as Rhodamine WT (CAS Registry No. 37299-86-8);1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol,also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5);fluorescein (CAS Registry No. 2321-07-5); fluorescein, sodium salt (CASRegistry No. 518-47-8, aka Acid Yellow 73, Uranine);2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4);1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and saltsthereof; 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) andsalts thereof; 1,8-anthracenedisulfonic acid (CAS Registry No.61736-92-3) and salts thereof; and mixtures thereof. The fluorescenttracers listed above are commercially available from a variety ofdifferent chemical supply companies.

In addition to the tracers listed above, those skilled in the art willrecognize that salts using alternate counter ions may also be used.Thus, for example, anionic tracers which have Na⁺ as a counter ion couldalso be used in forms where the counter ion is chosen from the list of:K⁺, Li⁺, NH₄ ⁺, Ca⁺², Mg⁺² or other appropriate counter ions. In thesame way, cationic tracers may have a variety of counter ions, forexample: Cl⁻, SO₄ ⁻², PO₄ ⁻³, HPO₄ ⁻²; H₂PO₄ ⁻; CO₃ ⁻²; HCO₃ ⁻; or otherappropriate counter ions.

Modifications of these tracers to control molecular weight or physicalsize within a desirable size range by, for example, affixing them to aninert polymeric molecule, incorporating them into a fluorescentmicrosphere or adding additional chemical moieties in the side chains ofthe molecules should be obvious to those skilled in the art. Suchmodifications are included herein.

As previously discussed, the inert tracer(s) is measured or detected toevaluate the performance of the membrane separation process. Adetermination of the presence of an inert fluorescent tracer and theconcentration thereof in the influent/feedwater and/or other processstream of a membrane separation process can be made when theconcentration of the inert tracer in the influent/feedwater and/or otherstream of a membrane separation system is several parts per million orless, even as low as parts per billion as previously discussed.

At times, it may be desired to employ a number of inert tracers. In thisregard, it may be desired to use a number of inert tracers to monitor,for example, inert tracer-specific losses, variances, like conditions orcombinations thereof. Such separate and distinct inert tracers can eachbe detected and quantified in a single influent/feedwater and/or otherstream faction despite both being inert fluorescent tracers providedthat their respective wavelengths of emission do not interfere with oneanother. Thus, concurrent analyses for multiple inert tracers ispossible by selection of inert tracers that have appropriate spectralcharacteristics.

The inert tracers of the present invention can be detected by utilizinga variety of different and suitable techniques. For example,fluorescence emission spectroscopy on a substantially continuous basis,at least over a given time period, is one of the preferred analyticaltechniques according to an embodiment of the present invention. Onemethod for the continuous on-stream measuring of chemical tracers byfluorescence emission spectroscopy and other analysis methods isdescribed in U.S. Pat. No. 4,992,380, B. E. Moriarty, J. J. Hickey, W.H. Hoy, J. E. Hoots and D. A. Johnson, issued Feb. 12, 1991,incorporated hereinto by reference.

In general, for most fluorescence emission spectroscopy methods having areasonable degree of practicality, it is preferable to perform theanalysis without isolating in any manner the tracer(s). Thus, there maybe some degree of background fluorescence in the influent/feedwaterand/or concentrate on which the fluorescence analysis is conducted. Thisbackground fluorescence may come from chemical compounds in the membraneseparation system (including the influent/feedwater system thereof) thatare unrelated to the membrane separation process of the presentinvention.

In instances where the background fluorescence is low, the relativemeasurable intensities (measured against a standard fluorescent compoundat a standard concentration and assigned a relative intensity, forinstance 100) of the fluorescence of the inert tracer versus thebackground can be very high, for instance a ratio of 100/10 or 500/10,when certain combinations of excitation and emission wavelengths areemployed even at low fluorescent compound concentrations. Such ratioswould be representative of a “relative fluorescence” (under likeconditions) of respectively 10 and 50. In an embodiment, theexcitation/emission wavelengths and/or the amount of inert traceremployed are selected to provide a relative fluorescence of at leastabout 5 or about 10 for the given background fluorescence anticipated.

Examples of fluorometers that may be used in the practice of thisinvention include the TRASAR® 3000 and TRASAR® 8000 fluorometers(available from Ondeo Nalco Company of Naperville, Ill.); the HitachiF4500 fluorometer (available from Hitachi through Hitachi InstrumentsInc. of San Jose, Calif.); the JOBIN YVON FluoroMax-3 “SPEX” fluorometer(available from JOBIN YVON Inc. of Edison, N.J.); and the GilfordFluoro-IV spectrophotometer or the SFM 25 (available from Bio-techKontron through Research Instruments International of San Diego,Calif.). It should be appreciated that the fluorometer list is notcomprehensive and is intended only to show examples of fluorometers.Other commercially available fluorometers and modifications thereof canalso be used in this invention.

It should be appreciated that a variety of other suitable analyticaltechniques may be utilized to measure the amount of inert tracers duringthe membrane separation process. Examples of such techniques includecombined HPLC-fluorescence analysis, colorimetry analysis, ion selectiveelectrode analysis, transition metal analysis and the like.

For example, the combination of high-pressure liquid chromatography(“HPLC”) and fluorescence analyses of inert fluorescent tracers can beutilized to detect measurable amounts of the inert tracer within themembrane separation system of the present invention, particularly whenvery low levels of the inert tracer are used or the backgroundfluorescence encountered would otherwise interfere with the efficacy offluorescence analysis. The HPLC-fluorescence analysis method allows theinert tracer compound to be separated from the fluid matrix and then theinert tracer concentration can be measured.

The HPLC method can also be effectively employed to separate an inerttracer compound from a fluid matrix for the purposes of then employingan inert tracer-detection method other than the fluorescence analysis.An example of this type of chromatographic technique is described in“Techniques in Liquid Chromatography”, C. F. Simpson ed., John Wiley &Sons, New York, pp. 121-122, 1982, incorporated herein by reference, and“Standard Method for the Examination of Water and Wastewater”, 17thEdition, American Public Health Association, pp. 6-9 to 6-10, 1989,incorporated herein by reference.

With respect to colorimetry analysis, colorimetry and/orspectrophotometry may be employed to detect and/or quantify an inertchemical tracer. Colorimetry is a determination of a chemical speciefrom its ability to absorb ultraviolet or visible light. Calorimetricanalysis techniques and the equipment that may be employed therefor aredescribed in U.S. Pat. No. 4,992,380, B. E. Moriarty, J. J. Hickey, W.H. Hoy, J. E. Hoots and D. A. Johnson, issued Feb. 12, 1991,incorporated herein by reference.

With respect to ion selective electrode analysis, an ion selectiveelectrode may be used to determine the concentration of an inertchemical tracer through the direct potentiometric measurement ofspecific ionic tracers in aqueous systems. An example of an ionselective electrode tracer monitoring technique is described in U.S.Pat. No. 4,992,380, B. E. Moriarty, J. J. Hickey, W. H. Hoy, J. E. Hootsand D. A. Johnson, issued Feb. 12, 1991, incorporated herein byreference.

It should be appreciated that analytical techniques for detecting and/orquantifying the presence and/or concentration of a chemical speciewithout isolation thereof are within an evolving technology. In thisregard, the above survey of analytical techniques suitable for use indetecting measurable amounts of the inert tracer during the membraneseparation process of the present invention may presently not beexhaustive. Thus, analytical techniques equivalent to the above forpurposes of the present invention may likely be developed in the future.

As previously discussed, the present invention can provide highlyselective and/or sensitive monitoring of a variety of process parametersunique and specific to the membrane separation process. The monitoringis based on the measurable amounts of an inert tracer analyzed duringthe membrane separation process. In this regard, the inert tracer can bedetected at any suitable location or locations within the membraneseparation process, such as any suitable position in a membranefiltration process along the feedwater stream, the concentrate stream,the permeate stream, the like or combinations thereof This effectivelycorresponds to a concentration of the inert tracer in each stream.

In an embodiment, the monitoring of the membrane filtration process ofthe present invention can be based on a measurable amount of the inerttracer from at least one of the feedwater stream, the permeate streamand the concentrate stream. For example, when the parameter of interestis the percent rejection (discussed below), it is believed that the mostsensitive determinations are of the feedwater inert tracer concentrationand the permeate inert tracer concentration (which will be zero if thepercent rejection is 100 percent). The percent rejection parameter, thatis, the percent of solute that has been rejected or has not passedthrough the membrane, can be determined by the following relationships:

C_(R)=C_(B)/C_(F)=F/B  Equation 1

F=P[C_(R)/(C_(R)−1)]  Equation 2

C_(R)[1/(1−R)]  Equation 3

where C_(F) is the concentration of solute in the feed stream (e.g.,combined fresh feed fluid and recycled feed fluid); C_(P) is theconcentration of solute in the permeate as discharged through; C_(B) isthe concentration of solute in the concentrate water as dischargedthrough; F is the feed stream flow rate in gal/min; P is the permeatedischarge flow rate in gal/min; B is the concentrate water flow rate; Lis the recycle rate; R is the recovery ratio (e.g., P/F); and C_(R) isthe concentration ratio, (e.g., C_(B)/C_(F)).

When there is less than complete rejection of a solute, for instanceonly 80 percent rejection (e.g., a 0.8 rejection factor), C_(R) will beless than F/B as shown in Equation 4:

C_(R)=(F/B)×rejection factor  Equation 4

The rejection factor again is the measure of the extent of soluterejection by the membrane, as calculated in Equation 5, wherein C_(F) isthe concentration of solute in the feedwater and C_(P) is theconcentration of solute in the permeate:

rejection factor=(C_(F)−C_(P))/C_(F)  Equation 5

The same equations will apply in a traced stream (e.g., a stream thatcontains an inert tracers)) wherein “tracer-C” (e.g., tracer-C_(F),tracer-C_(P) and tracer-C_(B)) is substituted for C_(F), C_(P) and C_(B)in equations 1-5. When there is less than complete rejection of an inerttracer, for instance only 80 percent rejection (a 0.8 rejection factor),tracer-C_(R) will be less than F/B as shown in Equation 4. In thisregard, the determination of the rejection of the inert tracer in themembrane filtration system is at least proportional to the rejection ofthe solute within same. In a preferred embodiment, the percent rejectionis determined and maintained at an amount ranging from about 95 to about100 percent.

In this regard, monitoring of an amount of the inert tracer as it mayvary during membrane filtration can be utilized to evaluate a number ofprocess parameters specific to membrane filtration such as a percentrecovery, percent rejection, recovery ratio or the like, with a highdegree of sensitivity, selectivity and accuracy, as previouslydiscussed. The ability to evaluate these types of membrane separationprocess parameters with such level of certainty, sensitivity andselectivity and on a continual basis in accordance with the presentinvention can provide a better understanding, in real time, of theperformance of the membrane. Thus, adjustments to the membraneseparation process can be made more responsively and effectively basedon the measured amount of the inert tracer, if needed, to optimizemembrane performance. For example, adjustments can be made to increasethe recovery ratio or percent recovery of the membrane separationsystem. In this regard, increasing the recovery ratio or percentrecovery, for unit product, will reduce the feedwater required and thusreduce feedwater costs, lower influent fluid pretreatment costs andchemical treatment requirements. It should be appreciated that theoptimal percent rejection value can vary with respect to the type ofmembrane separation system. In addition, percent recovery may becalculated in various ways. In membrane filtration the percent recoverycalculation can be based on ratios of the various streams or onconcentrations of solutes within those streams. In this regard, theamount of inert tracer in the various streams can provide an accurateassessment of percent recovery as well as a method for checking thecalibration of the mechanical flow sensors in the system.

However, unless controlled or optimally minimized, scaling and/orfouling of the membrane can adversely impact the performance of membraneseparation. If deposition on the membrane is neither prevented nordetected soon enough for effective removal by cleaning methods, thenormal life of the membrane, which can be about three to five years forreverse osmosis, may be severely shortened and replacement costsdramatically increased. As previously discussed, the membrane separationsystems are more sensitive to such scaling and/or fouling activity ascompared to cooling water systems. It should be appreciated that themembrane separation system of the present invention can include anysuitable type and amount of components in order to effectively treat thescale and/or fouling conditions, such as, any suitable treatment orpretreatment system including antiscalants and/or biofouling agents,filters, treatment equipment, such as chemical agent delivery devices,suitable like components or combinations thereof.

For example, suitable antiscalants that can be used in the membraneseparation system (especially reverse osmosis systems) of the presentinvention include suitable polymers in aqueous solution which inhibitthe formation and growth of alkaline earth carbonate and sulfate scales,including calcium carbonate (“CaCO₃”), calcium sulfate (“CaSO₄”) or thelike. Antiscalant chemicals are generally fed continuously into the feedstream wherein the optimum feed point is before a cartridge prefilterpositioned along the feedwater stream. The use of a continuous feed ofantiscalants can minimize or eliminate the need for acid to be fed intothe system in order to control scale, and can facilitate the suspensionof solids and colloids in solution. This can minimize membrane fouling,and inhibit the precipitation of CaCO₃ and CaSO₄.

In an embodiment, the present invention can monitor and/or control theconcentration of the scaling and/or fouling treatment agents within themembrane separation process based on the measurable amounts of the inertfluorescent tracer in the system. In an embodiment, the inert tracer iscontinuously fed to the feedwater along with the treatment agents. Itshould be appreciated that the inert tracer can be added separately oras a part of a formulation of the treatment agent to the feedwater. Inan embodiment, the inert tracer is fed to the feedwater in knownproportion to the scaling and/or biofouling agent In this regard, themeasure of the inert tracer concentration corresponds to (isproportional to) the chemical concentration (underzero-system-consumption conditions) at any suitable tracer monitoringpoint within the membrane separation system.

The chemicals or treatment agents employed as antiscalants and/oranti-fouling agents, and the mechanisms by which they inhibit scaledeposition, may change as improvements are made in antiscalant chemistryfor membrane filtration systems, but the need for a continuous feed oftreatment agents will most likely continue despite the improvements.

As previously discussed, inert tracers of the present invention can beutilized to monitor a variety of different parameters specific tomembrane separation such that the performance of membrane separationprocesses can be effectively monitored and controlled. In an embodiment,the parameters can include normalized permeate flow and percentrejection (as discussed above). In this regard, the present inventioncan be utilized to assess and/or control a variety of different processconditions that can impact membrane performance, for example, scalingand/or fouling conditions, membrane leakage, degradation and the likespecific to the membrane separation process as previously discussed.

It should be appreciated that the preferred inert tracers of the presentinvention, substantially have a rejection factor of 1, and morepreferably are employed in minute concentrations. Thus, the use of theinert tracer of the present invention does not in any significant manneradd to the total dissolved solids (“TDS”) of the permeate nordetrimentally effect a downstream ion exchange process or other permeatepolishing process.

Normalized Permeate Flow Monitoring

The normalized permeate flow is typically considered a sensitiveforecaster of trouble in a membrane filtration process, such as reverseosmosis. In this regard, a reduction of the permeate flow rate is astrong indicator of membrane fouling, whereas its increase is a strongindicator of membrane degradation, for instance due to an adverseoperation condition. In reverse osmosis the actual permeate flow ratecan vary with respect to the feed stream temperature, driving force andfeedstream TDS. Normalized permeate flow is determined through a simplecalculation which eliminates the effect of actual system temperature anddriving force variations and converts the actual permeate flow readingsto what they would be if the system were operating at constant(“normal”) driving force and temperature conditions, which are routinelythe start-up driving force and 25° C. The actual permeate flow rate isconventionally a direct reading from a permeate flowmeter. Thetemperature conversion factor for a given feedwater temperature isprovided by the membrane manufacturer for each specific membrane.

Normalized Permeate Flow Example

In reverse osmosis systems employing differential pressure as thedriving force, the feed pressure and permeate pressure variations arereduced to a differential pressure conversion factor which includes thestart-up net pressure divided by the actual net differential pressure(e.g., a differential pressure calculated by subtracting the permeatepressure from the feed pressure, which in turn can be measured from anysuitable pressure meters). The permeate flow rate is multiplied by thetemperature conversion factor and the driving pressure conversionfactor. Applicants have discovered that the monitoring of the inerttracer of the present invention can be used to enhance normalized flowmonitoring.

The monitoring of inert tracer concentrations in the feedwater and theconcentrate can provide a measure of actual permeate flow, which will bethe difference between total flow (e.g., the feedwater flow which aninert tracer measures) and concentrate flow (which an inert tracer alsomeasures). The inert tracer monitorings of the present invention, thus,can provide a measure of actual permeate flow in addition to thereadings from the usual flow meter. With a combination of normalizedpermeate flow determinations and driving force measures, severalcritical trends can be readily detected. If the normalized permeate flowis dropping while the driving force is increasing, this signals membranefouling. If, instead, the normalized permeate flow is dropping while thedriving force remains the same there is a forewarning to check thegauges and the like for accuracy.

As previously discussed, there exists a relationship between the flowrate and the concentration of the inert tracer such that the water flowcan be determined based on the measurable amount of the inert tracer inthe membrane separation system. The flow rate of any membrane separationprocess stream is the volume that passes a given point within a giventime period. The monitoring of the concentration of an inert tracer in astream at a given point, thus, can provide a determination of flow rateby mass balance of inert tracer ions in solution compared to inerttracer added. Alternatively, since the mass flow rates of the dischargestreams, in combination, must equal the mass flow rate of the feedstream, and the mass of the inert tracer in the discharge streams, incombination, must equal the mass of the inert tracer in the feedstream,flow rates and/or inert tracer concentrations of one of such streams canbe calculated from the others, when known. Moreover, when an inerttracer is added to the feedwater at a known rate (e.g., amount per unittime), the concentration of an inert tracer in the feedwater as itpasses the feedwater tracer monitoring point itself can determine theflow rate of the feed stream.

Differential Pressure Monitoring

In membrane filtration, the differential pressure is the differencebetween the feed pressure and the concentrate pressure. It is a measureof the hydraulic pressure losses through the membrane-filtrationmembrane elements and the manifold piping. When the feed stream flowchannels become clogged, the driving force increases. The differentialpressure also depends upon the feedstream flow rate and the percentrecovery. An accurate comparison between differential pressure readingstaken at different times requires that the membrane filtration system isoperating at the same percent recovery and feed flow rate in eachinstance. In this regard, inert tracer monitoring can be utilized toaccurately assess the differential pressure of the membrane separationsystem. It should be appreciated that the differential pressure at anygiven point in time can be determined by conventional methods.

Percent Rejection Monitoring

The percent rejection is the percentage of solute(s) that is rejected bythe membrane separation process. In practice, a percent rejection isbased on one or more selected solutes rather than the entirety ofsolutes in the feedwater, and the percent rejection value can include anaccompanying identification of the reference solute(s). The percentrejection often will change upon the onset of a membrane and/or systemproblem, such as fouling, scaling, membrane hydrolysis, improper pH, toolow of a feed pressure, too high of a recovery rate, a change in thecomposition of the influent fluid source, a leaking “O” ring and thelike. Typically, a decrease in percent rejection can indicate problemsassociated with membrane performance. However, the percent rejection mayincrease upon membrane clogging by certain foulants. In membranefiltration the percent rejection is the rejection factor (e.g., Equation5) expressed as a percentage (e.g., multiplied by 100). The presentprocess permits the percent rejection to be determined almostinstantaneously, using Equation 6 as follows:

rejection factor=(tracer-C_(F)−tracer-C_(P))/tracer-C_(F)  Equation 6

where the virtually instantaneous and continuous monitorings of thefeedwater inert tracer concentration and the permeate inert tracerconcentration can be determined with a high degree of selectivity,sensitivity and accuracy as previously discussed. Since the feedwaterinert tracer concentration (tracer-C_(F)) effectively varies little incontrast to other feedwater solutes (whose concentrations vary withfeedwater quality fluctuations), and since the inert tracer can bedetected more accurately at low levels than most all other solutes, lessnatural data variation (e.g., variations arising from feedwaterconcentration variations) can exist with the method of the presentinvention as compared to conventional percent recovery monitoringtechniques that typically measure the concentration of solutes todetermine percent recovery. This reduction in natural data variationmakes subtle trends easier to identify.

It should be appreciated that the present invention can be utilized toassess and/or control a variety of different conditions that may have animpact on the performance of the membrane separation process. Forexample, the present invention can be utilized to monitor leaks in themembrane elements. This is very important to the practical operation ofa membrane separation system.

In this regard, leakage of concentrate through a membrane itself or acomponent of the membrane element contaminates the permeate. Permeatecontamination by virtue of leakage may at times be so severe that theperformance of the membrane separation process is substantiallyimpaired, and at best the quality of the permeate is diminished. Uponsuch leakage there will be an increase in the normalized permeate flowand permeate solute concentrations, but the increases may be minor andmost probably not be detected for at least a number of hours ifconventional monitoring techniques are utilized.

Applicants have discovered that the present invention can monitormembrane leakage with a high degree of sensitivity, selectivity and/oraccuracy and that can be readily conducted on a continuous basis. Forinstance, if under normal conditions a reverse osmosis system isproducing a 75/25 ratio of parts by weight of permeate to parts byweight of concentrate (e.g., the permeate having 40 ppm TDS and theconcentrate having 2000 ppm TDS) a leakage of 1 percent of theconcentrate (e.g., 0.75 parts) into the permeate would increase theweight of the permeate by only 3 percent. Such increase would bedifficult to detect solely by conventional methods of monitoring thenormalized permeate flow. If undetected, such a leak would then doublethe permeate TDS to about 97 ppm. When the inert fluorescent tracermonitoring of the present invention is utilized to monitor the permeate,particularly on a continuous or substantially continuous basis, anincrease in permeate inert tracer concentration can be readily detectedto signal that leakage is likely to be occurring. In addition, thedetection of an increase in the concentration of permeate inert tracerwould follow the onset of the leakage almost instantaneously.

When a reverse osmosis system employs a number of membrane elements, theproduced permeate from each are often combined before permeate qualityscreening. An increase in permeate TDS from a single membrane element isless detectable by a determination of TDS with respect to the combinedpermeates because of the dilution effects. In addition, the TDS increasein the combined permeates does not indicate the site of the leakage.When the present process is employed to monitor permeate inert tracerconcentration, the separate permeates produced by each membrane elementcan easily be monitored before the permeates are combined. Not only canthe present process detect the leakage, but it can also be utilized todetermine the location of the leak.

In addition to the monitoring capabilities of the present inventiondiscussed above, a number of different other process conditions ofmembrane separation systems can also be monitored by the presentinvention on a regular or continuous basis to provide a real-timeassessment of membrane performance. These conditions can include, forexample, concentrate flow rate, percent recovery and biocideconcentration. In this regard, the SDI measures the quantity ofparticulate contamination in waters by particles about 0.45 micron indiameter or greater. In an embodiment, the concentrate flow rate andpercent recovery can be monitored with a single inert tracer asdiscussed above. In an embodiment, the biocide concentration can be mosteffectively monitored using a separate inert tracer.

The methods of the present invention can include any suitable type,number and combination of components, such as inert tracer compounds,inert tracer detection devices (e.g., analytical techniques) or thelike. In an embodiment, the chemical compound(s) selected as the inerttracer(s) is soluble in the membrane separation stream to which it isadded to the concentration value desired and is substantially stable inthe environment thereof for the useful life expected of the inerttracer(s). In a preferred embodiment, the combination of the chemicalcompound(s) selected as the inert tracer(s) and the analytical techniqueselected for determining the presence of such inert tracer(s), permitssuch determination without isolation of the inert tracer(s), and morepreferably should permit such determination on a continuous and/oron-line basis.

In an embodiment, the present invention includes a controller (notshown) to monitor and/or control the operating conditions and theperformance of the membrane separation process based on the measurableamount of inert fluorescent tracer(s). The controller can be configuredand/or adjusted in a variety of different and suitable ways.

For example, the controller can be in contact with the detection device(not shown) to process the detection signal (e.g., filter noise from thesignal) in order to enhance the detection of the inert tracer. Further,the controller can be adjusted to communicate with other components ofthe membrane separation system. The communication can be either hardwired (e.g., electrical communication cable), a wireless communication(eg., wireless RF interface), a pneumatic interface or the like.

In this regard, the controller can be utilized to control theperformance of membrane separation. For example, the controller cancommunicate with a feed device (not shown) in order to control thedosage of treatment agents, such as antiscalants and biocides, withinthe membrane separation process. In an embodiment, the controller iscapable of adjusting the feed rate of the feed stream based on theamount of inert tracer that is measured.

It should be appreciated that pairs or groups of inert tracer monitoringpoints that are to be compared should not be positioned across aflow-through site that has a high concentration of solids, for instancea solids concentration of at least about 5 or about 10 weight percentper unit volume based on a measured volume unit of about one cubic inch.Such high solids concentration flow-through sites are found at the siteof filter cakes and the like. In this regard, these sites may absorb, orselectively absorb, at least some amount of the inert tracer. This candistort the significance of monitoring comparison. When an inert traceris added upstream of, for instance, a cartridge filter, in anembodiment, the first monitoring location of a monitoring pair shouldpreferably be downstream of such sites.

However, separate monitorings across a flow-through site of high solidsconcentration may be conducted to determine the loss of an inert tracerfrom the fluid, and if such loss is nonselective for the inert tracer,the loss of other solutes at that site. For instance, when theflow-through site is a cartridge filter, such monitorings can determinethe loss of solutes, if any, attributable to that pretreatment location.Other high solids concentration sites include without limitation sitesof solids concentration(s) created by the use of chemical additives suchas coagulants, flocculants and the like.

In an embodiment, the inert tracer selected is not a visible dye, thatis, the inert tracer is a chemical specie that does not have a strongabsorption of electromagnetic radiation in the visible region, whichextends from about 4000 Angstroms to about 7000 Angstroms (from about400 nanometers (“nm”) to about 700 nm). Preferably the tracer is chosenfrom a class of materials which are excited by absorption of light andproduct fluorescent light emission, where the excitation and emissionlight occurs at any point within the far ultraviolet to near infraredspectral regions (wavelengths from 200-800 nm). The relativefluorescence intensity of the inert tracer must be such that it isdetectable in the amounts specified by product formulations (typically2-10 ppb as active fluorophore when dosed into the feed water stream ofa device).

Alternatively, when the tracer dye does have strong adsorbtions in thevisible spectrum, it is used in concentrations such that it is notdetectable to the naked eye. Such embodiments may be preferred, forinstance, when a membrane's percent rejection of the tracer is less than100 percent, and it is desirable to produce a permeate free of color.

In some instances, it may be preferable to chose a fluorophore whichemits visible fluorescent light when excited by UV light. This may bepreferred when visual detection and/or photographic or other imaging ofthe system is desired.

Although membrane separation systems are often employed for thepurification of water, or the processing of aqueous streams, the systemsof the present invention are not limited to the use of an aqueousinfluent. In an embodiment, the influent may be another fluid, or acombination of water and another fluid. The operational principles ofmembrane separation systems and processes of the present invention arenot so governed by the nature of the influent that the present inventioncould not be employed with influents otherwise suitable for waterpurification in a given membrane separation system. The descriptions ofthe invention above that refer to aqueous systems are applicable also tononaqueous and mixed aqueous/nonaqueous systems.

In an embodiment, the inert fluorescent tracer monitoring methods of thepresent invention can be utilized to monitor membranes which aresubjected to destructive (sacrificial) testing. This type of testing mayinclude the sectioning or division of an industrial membrane, forinstance by cutting, into a number of separate membrane pieces prior totesting so that a number of tests can be performed, each on a differentsection of the membrane. In this regard, the inert fluorescent tracermonitoring of the present invention can be utilized to monitor a numberof different parameters of destructive testing including, withoutlimitation, the effects of excessive pressure, contact with amembrane-destructive fluid and the like. The diagnostic regime of thedestructive testing would generally be focused on the membrane which maybe subjected to visual inspection of its surface, a membrane-surfacemicrobiological analysis by swabbing of its surface and analysis ofwater samples in contact with membrane, surface analysis for inorganicdeposits by SEM/EDS, surface analysis for organic deposits by IR,electron microscopy, ICP and like surface analysis techniques.

Although the membrane during destructive testing is not on-line, in anembodiment of the present invention the inert tracer can be added to afluid stream which flows to the membrane and passes by or through it asa first effluent stream to exit as a second effluent stream. The inerttracer can be added to the fluid upstream of the membrane and the inerttracer in the fluid stream at least passes by the membrane as acomponent of the first effluent stream and/or passes through themembrane to exit as a component of the second effluent stream. The inerttracer is monitored in the fluid stream at a point before the membraneto determine an influent inert concentration value, and/or in at leastone of the first and the second effluent streams to determine aneffluent inert tracer concentration. In this regard, the inert tracer isrepresentative of a solute of the fluid stream that can be added to thefluid in an amount sufficient for the determinations of influent inerttracer concentration and effluent inert concentration. Thus, theseparation performance of the membrane can be determined prior to actualuse.

“Deposits” is meant herein to refer to material that forms and/orcollects on surfaces of a membrane. The “amount” or “concentration” ofinert tracer is meant herein to refer to the concentration of the inerttracer in the specified fluid in terms of weight of the inert tracer perunit volume of the fluid, or weight of the inert tracer per unit weightof the fluid, or some characteristic of the inert tracer that isproportional to its concentration in the fluid and can be correlated toa numerical value of the inert tracer concentration in the fluid(whether or not that correlation conversion is calculated), and can be avalue of zero or substantially zero. Thus, the process of the presentinvention includes the detection of the absence of such chemicalspecies, at least to the limitations of the analytical method employed.

The foregoing descriptions of the present invention at times referspecifically to aqueous influents and effluents, and the use of anaqueous system for describing a membrane filtration system and theoperation of the present invention therein is exemplitive. A person ofordinary skill in the art, given the disclosures of the presentspecification, would be aware of how to apply the foregoing descriptionsto nonaqueous membrane filtration systems.

“Treatment chemicals and/or agents” is meant herein without limitationto include treatment chemicals that enhance membrane separation processperformance, antiscalants that retard/prevent membrane scale deposition,antifoulants that retard/prevent membrane fouling, biodispersants,microbial-growth inhibiting agents, such as biocides and cleaningchemicals that remove membrane deposits.

It should be appreciated that the present invention is applicable to allindustries that can employ membrane separation processes. For example,the different types of industrial processes in which the method of thepresent invention can be applied generally include raw water processes,waste water processes, industrial water processes, municipal watertreatment, food and beverage processes, pharmaceutical processes,electronic manufacturing, utility operations, pulp and paper processes,mining and mineral processes, transportation-related processes, textileprocesses, plating and metal working processes, laundry and cleaningprocesses, leather and tanning processes, and paint processes.

In particular, food and beverage processes can include, for example,dairy processes relating to the production of cream, low-fat milk,cheese, specialty milk products, protein isolates, lactose manufacture,whey, casein, fat separation, and brine recovery from salting cheese.Uses relating to the beverage industry including, for example, fruitjuice clarification, concentration or deacidification, alcoholicbeverage clarification, alcohol removal for low-alcohol contentbeverages, process water, and uses relating to sugar refining, vegetableprotein processing, vegetable oil production/processing, wet milling ofgrain, animal processing (e.g., red meat, eggs gelatin, fish andpoultry), reclamation of wash waters, food processing waste and thelike.

Examples of industrial water uses as applied to the present inventioninclude, for example, boiler water production, process waterpurification and recycle/reuse, softening of raw water, treatment ofcooling water blow-down, reclamation of water from papermakingprocesses, desalination of sea and brackish water for industrial andmunicipal use, drinking/raw/surface water purification including, forexample, the use of membranes to exclude harmful micro-organisms fromdrinking water, polishing of softened water, membrane bio-reactors,mining and mineral process waters.

Examples of waste water treatment applications with respect to the inerttracer monitoring methods of the present invention include, for example,industrial waste water treatment, biological waste treatment systems,removal of heavy metal contaminants, polishing of tertiary effluentwater, oily waste waters, transportation related processes (e.g., tankcar wash water), textile waste (e.g., dye, adhesives, size, oils forwool scouring, fabric finishing oils), plating and metal working waste,laundries, printing, leather and tanning, pulp and paper (e.g., colorremoval, concentration of dilute spent sulfite liquor, lignon recovery,recovery of paper coatings), chemicals (e.g., emulsions, latex,pigments, paints, chemical reaction by-products), and municipal wastewater treatment (e.g., sewage, industrial waste).

Other examples of industrial applications of the present inventioninclude, for example, semiconductor rinse water processes, production ofwater for injection, pharmaceutical water including water used in enzymeproduction/recovery and product formulation, and elect coat paintprocessing.

Examples of diagnostics which can be determined by the use of inerttracers include, but are not limited to, effective “residence times” forspecies within the membrane, system flow profiles, membrane damagedetection, system recovery based on mass balance, detection of scalingor fouling tendency (based on differences between mass balance and flowbased system parameters), system volume calculation, chemical treatmentproduct distribution and feed variability.

EXAMPLES

The following examples are intended to be illustrative of the presentinvention and to teach one of ordinary skill how to make and use theinvention. These examples are not intended to limit the invention or itsprotection in any way.

Example 1

Tests were performed using a multi-stage reverse osmosis system. Thesystem utilized six pressure vessels, arranged in a 2:2:1:1configuration with each pressure vessel containing 3 spiral woundmembrane elements. The membrane elements were a polyamide based elementsfrom several element manufacturers. Typical system recovery, based onsystem flows, was 75-80%, with the feed flow ranging from about 100 toabout 130 gpm.

The feed water included an inert fluorescent tracer (an aqueous solutionof 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PTSA)), dilutedwith water to give a final concentration of 0.20 to 0.25% as the activefluorophore in an aqueous solution. The inert tracer was fed into the ROmembrane system using a positive displacement pump at a feed rate ofapproximately 2 milliliters/minute and at a concentration of about 6 ppminto the feed stream described above.

The concentration of the inert tracer was fluorometrically measured(with a TRASAR® 3000 and/or a TRASAR® 8000 fluorometer) in the ROmembrane system in both the feed stream and the concentrate stream overa select period of time, generally one to three hours with data beingcollected at one second intervals. (Fluorometer readings were expressedas “ppm of treatment product.” The fluorometer was programmed to readthe concentration of the tracer and convert the reading into ppm oftreatment. In this case, the treatment was assumed to contain 0.2%active fluorophore.) Periodic fluctuations in the concentration of theinert tracer in both of the concentrate and feed streams werecontinuously detected. For example, the concentration of the inerttracer in the concentrate stream varied from about 40 ppb of tracer (20ppm as treatment product) to as high as about 180 ppb of tracer (90 ppmas treatment product). In general the concentration of the inert tracerin the concentrate stream varied between about 40 ppb of tracer (20 ppmas treatment product) and about 80 ppb of tracer (40 ppm as treatmentproduct). In comparison, the concentration of the inert tracer in thefeed stream varied from about 10 ppb of tracer (5 ppm as treatmentproduct) or less to as high as about 130 ppb of tracer (65 ppm astreatment product). In general, the concentration of the inert tracer inthe feed stream varied from about 10 ppb of tracer (5 ppm as treatmentproduct) or lower to about 20 ppb of tracer (10 ppm as treatmentproduct).

The ability of the present invention to detect fluctuations in theconcentration of the inert tracer added to the membrane separationsystem uniquely allows the present invention to evaluate processparameters specific to a membrane separation with a high degree ofselectivity, sensitivity and/or accuracy such that the performance(e.g., operational, chemical, mechanical and/or the like) of membraneseparation can be effectively monitored. In this regard, suitableadjustments can be controllably and responsively made to the membraneseparation system such that performance is optimized. For example, thedetection of fluctuations in the concentration of the inert fluorescenttracer during membrane separation (as discussed above) may necessarilyindicate that suitable and responsive adjustments to the membraneseparation process are necessary to decrease the fluctuations, and, thusenhance membrane separation performance.

The test results also displayed spikes in the concentration of the inerttracer in both of the feed stream and the concentrate stream. Aspreviously discussed, the spike in the amount of inert tracer in thefeed stream occurred at about 120 ppb of tracer (60 ppm as treatmentproduct) in comparison to that in the concentrate stream which occurredat about 180 ppb of tracer (90 ppm as treatment product). By measuringthe elapsed time between the spikes in both of the feed and concentratestreams, the effective residence time of solutes within the membraneseparation system can be calculated. This information can be useful, forexample, in developing a treatment strategy specific to membraneseparation.

Furthermore, the tracer was used to calculate percent recovery asdescribed above. Whereas the percent recovery calculations based on flowmeasurements indicate recoveries of about 35% to about 80%, recoverycalculations based on mass balance of the tracer shows significantlyhigher percent recovery values (89-92%). Such information is useful indeveloping effective scale control strategies.

Example 2

Experiments were performed using thin film composites of a polyamidebased reverse osmosis membrane material in order to simulate processconditions utilizing a reverse osmosis membrane separation system.

In this regard, a number of flat or planar sheets of the membrane werecut from a roll of the polyamide material which is a commerciallyavailable product, for example FT30 from FILMTEC of Minneapolis, Minn.

Tests were performed in a SEPA CF, flat plate reverse osmosis cell whichis commercially available from the Osmonics Corporation of Minnetonka,Minn. In general, the test system included a feed water tank, a highpressure pump, and the flat plate cell. The system was modified so thatthe change in pressure across the membrane and the inlet pressure, aswell as the feedwater, permeate water, and concentrate waterconductivities, and the permeate and concentrate water flows could becontinuously monitored. A data logger, available from the YokogawaCorporation of America of Newnan, Ga., was used to continuously monitorand collect data. Fluorometers (TRASAR® 3000, TRASAR® 8000 and HitachiF-4500) were used to measure the concentrations of tracers in thesystems.

The experimental test conditions were as follows:

NaHCO₃ 118 ppm CaCl₂ 694 ppm MgSO₄ 7H₂O 1281 ppm Na₂HPO₄ 2.82 ppm pH 8.5

Permeate was sent to drain and concentrate returned to the feed watertank. The test was designed to form scale on the membrane over time,thus decreasing permeate flow.

Tests were run to show monitoring of the reverse osmosis system with anundamaged membrane. As shown by the calculated performance parameters inTable 2 below, the percent rejection of the tracer was 100%. Thisindicates that the tracer molecule did not pass through an undamagedmembrane. In contrast, a portion of the dissolved salts (as measured byconductivity) did pass through the membrane.

TABLE 1 Measured Parameters Tracer concentrations Temperature (ppm)Conductivity (mS) (Degrees) Flow (ml/min) Pressure (psi) feed rejectpermeate feed reject permeate F. C. reject permeate feed feed rejectpermeate 0.586 0.647 0.000 4.13 4.83 0.278 64 18 101 16.4 117 380 379 00.504 0.570 0.000 4.00 4.66 0.203 70 21 100 19 119 380 379 0 0.429 0.4650.000 5.49 6.15 0.151 66 19 100 11.8 112 380 379 0

TABLE 2 Calculated Parameters Percent Rejection Based on System VariousMeasures Normalized Inert Percent Recovery Based on Permeate Avg.Florescent Various Measures Flow Pressure Tracer Conductivity NPF TracerConductivity (NPF) Drop 100.0 93.3 14.0 9.4 15.4 20 1 100.0 94.9 16.011.6 14.8 21 1 100.0 97.2 10.6 7.7 11.0 14 1

Another sheet of polyamide membrane material was damaged by swabbing thesurface with a 0.05% hypochlorite solution. Using a feed solution of1500 ppm NaCl rejection of the tracer molecule was monitored. All otherexperimental conditions were the same as above. The results shown belowin Table 4 indicate significant passage of the tracer through thedamaged membrane. Since conductive salts pass through both undamaged(Table 2) and damaged (Table 3) membranes, the tracer only passesthrough damaged membranes, making tracer measurement a more sensitiveindicator of membrane damage than conductivity measurements.

TABLE 3 Measured Parameters Tracer concentrations Temperature (ppm)Conductivity (mS) (Degrees) Flow (ml/min) Pressure (psi) feed rejectpermeate feed reject permeate F. C. reject permeate feed feed rejectpermeate 0.604 0.633 0.000 5.02 5.25 0.182 77 25 242 13.9 256 380 379 00.605 0.655 0.140 5.02 5.36 1.470 73 23 177 16.5 194 380 379 0 0.6050.655 0.081 5.02 5.36 0.970 73 23 176 15.7 192 380 379 0

TABLE 4 Calculated Parameters Percent Rejection Based on System VariousMeasures Normalized Inert Percent Recovery Based on Permeate Avg.Florescent Various Measures Flow Pressure Tracer Conductivity NPF TracerConductivity (NPF) Drop 100.0 96.4 5.4 4.6 4.5 14 1 76.9 70.7 8.5 9.78.7 18 1 86.6 80.7 8.2 8.7 7.7 17 1

While the present invention is described above in connection withpreferred or illustrative embodiments, these embodiments are notintended to be exhaustive or limiting of the invention Rather, theinvention is intended to cover all alternatives, modifications andequivalents included within its spirit and scope, as defined by theappended claims.

What is claimed is:
 1. A method of monitoring a membrane separationprocess in an industrial water system comprising the steps of: (a)providing a membrane capable of removing solutes from a feed stream;wherein the membrane separates the feed stream into a concentrate streamwith a greater amount of solutes in it and a permeate stream with alesser amount of solutes in it; wherein said membrane is suitable foruse in an industrial water system; (b) adding an inert fluorescenttracer to the feed stream wherein said fluorescent tracer is notappreciably or significantly affected by the chemistry of the industrialwater system; wherein the concentration of the inert fluorescent tracerin the feed stream is from about 5 ppt to about 1000 ppm; (c) removingsolutes from the feed stream by contacting the membrane with the feedstream and having the membrane separate the feed stream into a permeatestream and a concentrate stream; (d) providing a fluorometer to detectthe fluorescent signal of the inert tracer in at least one of thepermeate stream and the concentrate stream; and (e) using the detectedfluorescent signal of the inert tracer to determine the amount of theinert fluorescent tracer in at least one of the permeate stream and theconcentrate stream.
 2. The method of claim 1 further comprising the stepof (f) evaluating a process parameter of the membrane separation processbased on the amount of the inert fluorescent tracer that is measured. 3.The method of claim 2 further comprising the step of (g) adjusting theoperating conditions of the membrane separation process based on theevaluation of a process parameter conducted in step (f).
 4. The methodof claim 2 wherein the process parameter evaluated is the removal ofsolutes from the feed stream based on the amount of the inert tracerthat is detected and measured in the permeate stream and in theconcentrate stream.
 5. The method of claim 1 wherein the membraneseparation process is selected from the group consisting of a cross-flowmembrane separation process and a dead-end flow membrane separationprocess.
 6. The method of claim 1 wherein the membrane separationprocess is selected from the group consisting of reverse osmosis,ultrafiltration, microfiltration, nanofiltration, electrodialysis,electrodeionization, pervaporation, membrane extraction, membranedistillation, membrane stripping, membrane aeration and combinationsthereof.
 7. The method of claim 1 wherein the inert fluorescent traceris selected from the group consisting of 3,6-acridinediamine,N,N,N′,N′-tetramethyl, monohydrochloride; 2-anthracenesulfonic acidsodium salt; 1,5-anthracenedisulfonic acid; 2,6-anthracenedisulfonicacid; 1,8-anthracenedisulfonic acid;anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol,16,17-dimethoxy-,bis(hydrogen sulfate), disodium salt;bathophenanthrolinedisulfonic acid disodium salt; amino 2,5-benzenedisulfonic acid; 2-(4-aminophenyl)-6-methylbenzothiazole;1H-benz[de]isoquinoline-5-sulfonic acid,6-amino-2,3-dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt;phenoxazin-5-ium, 1aminocarbonyl)-7-(diethylamino)3,4-dihydroxy-,chloride; benzo[a]phenoxazin-7-ium, 5,9-diamino-, acetate;4-dibenzofuransulfonic acid; 3-dibenzofuransulfonic acid;1-ethylquinaldinium iodide; fluorocein; fluorescein, sodium salt;Keyfluor White ST; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt; C.I. Florescent Brightener 230; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino],tetrasodium salt; 9,9′-biacridinium, 10,10′-dimethyl-, dinitrate;1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-ribitol;mono-, di-, or tri-sulfonated napthalenes selected from the groupconsisting of 1,5-naphthalenedisulfonic acid, disodium salt (hydrate);2-amino-1-naphthalenesulfonic acid; 5-amino-2-naphthalenesulfonic acid;4amino-3-hydroxy-1-naphthalenesulfonic acid;6-amino-4-hydroxy-2-naphthalenesulfonic acid;7-amino-1,3-naphthalenesulfonic acid, potassium salt;4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid;5-dimethylamino-1-naphthalenesulfonic acid; 1-amino-4-naphthalenesulfonic acid; 1-amino-7-naphthalene sulfonic acid; and2,6-naphthalenedicarboxylic acid, dipotassium salt;3,4,9,10-perylenetetracarboxylic acid; C.I. Fluorescent Brightener 191;C.I. Fluorescent Brightener 200; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl), dipotassiumsalt; benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2(2-phenylethenyl)-, sodium salt;1,3,6,8-pyrenetetrasulfonic acid, tetrasodiun salt; pyranine; quinoline;3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide; xanthylium,9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt;phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride; C.I.Fluorescent Brightener 235; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt; xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-,inner salt, sodium salt; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodiun salt; Tinopol DCS; benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis, disodium salt;benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt;7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt;and all ammonium, potassium and sodium salts thereof; and all mixturesthereof, wherein said components of said mixtures are selected such thatthe fluorescent signals of the individual inert fluorescent tracerswithin the mixture are capable of being detected.
 8. The method of claim1 wherein the inert fluorescent tracer is introduced into the feedstream in an amount from about 1 ppb to about 50 ppm.
 9. The method ofclaim 1 wherein the inert fluorescent tracer is introduced into the feedstream in an amount from about 5 ppb to about 50 ppb.
 10. The method ofclaim 1 wherein the inert fluorescent tracer is added to a treatmentchemical formulation in a known proportion to create a tracedformulation and it is this traced formulation that is subsequently addedto the feed stream; wherein the treatment chemical formulation isselected from the group consisting of antiscaling and antibiofoulingagents.
 11. The method of claim 1 wherein the industrial water system isselected from the group consisting of raw water processes, waste waterprocesses, industrial water processes, municipal water treatment, foodand beverage processes, pharmaceutical processes, electronicmanufacturing, utility operations, pulp and paper processes, mining andmineral processes, transportation-related processes, textile processes,plating and metal working processes, laundry and cleaning processes,leather and tanning processes, and paint processes.